Water-cooled catalyst system

ABSTRACT

The invention concerns a system (20) used to reduce pollutant emissions in the form of hydrocarbons, carbon monoxides and nitric oxides from internal combustion engines, in particular from ships&#39; engines or stationary engines. The catalyst housing (40) is covered by a gas-insulation hood (24) which is open upstream for the waste gas (18) to be decontaminated and is closed downstream. The gas-insulation hood (24) comprises a water cooler (28) which at least in some cases rests on the exterior thereof. The gas-insulation hood (24) preferably takes the form of a baffle silencer of known type of construction.

BACKGROUND OF THE INVENTION

The invention relates to a water-cooled catalyst system for reducing theemission of pollutants in the form of hydrocarbons, carbon monoxides andnitrous oxides from fuelled combustion engines, in particular shipengines or stationary engines

An auto-ignition or a fuelled combustion engine with an externalignition system essentially generates carbon dioxide but also carbonmonoxide, nitrous oxides and hydrocarbons which are emitted in theexhaust gases. Whereas the carbon and nitrous oxides are chemicallydefined compounds, the hydrocarbons comprise a large number ofcompounds.

Today, increasingly strict exhaust gas standards are being passed whichnow allow only very small residual quantities of the said toxic gases.This applies not only to car engines but increasingly also to shipengines and stationary engines. In particular, the increasing numbers ofmotor boats travelling on lakes and rivers will in the near future besubject to stricter regulations which allow scarcely any exhaustemissions from engines presently in use.

Exhaust cleaning technologies of petrol driven engines focus oncatalysts controlled by a lambda probe, in particular three-waycatalysts, but depending on the country also oxidation and/or double bedcatalysts. These catalysts reach a high temperature in the range from900° to 1000° C. after a short time, i.e. they develop a great heatradiation and must lie out of human reach. In cars this is not aproblem, the catalysts are safely arranged below the vehicle floor at arelatively large distance from the engine, and exposed to cooling airflows. A boat engine however only allows catalytic exhaust gasdetoxification if the catalyst is fitted in the immediate vicinity ofthe engine, where there is largely no cooling wind. In view of the heatdeveloped by the catalyst and the associated risk of fire, despite thewide range on the market almost no boat engines can be found withcatalytically cleaned exhaust gases. This is all the moredisadvantageous as it is naturally more difficult for a boat to escapequickly and completely from its own exhaust gas cloud. In unfavourablewind conditions, such an exhaust gas cloud can accompany the boat forrelatively long periods.

EP, B1 0314129 describes a catalyst system for petrol engines, usingwhich exhaust gases from boat engines can be treated even when theinjection mixture is rich, i.e. with high CO and HC emissions. This isaimed in particular at boat engines which are operated with very highlambda values of between 0.75 and 0.90. To solve the problem, a catalystsystem is used with a reductive part lying upstream in the exhaust gasflow and an oxidative catalyst part lying downstream, with a purelyaxial guidance of the exhaust gas through the catalyst parts. Thecatalyst is surrounded by a water-cooled housing, so it cannot develop agreat heat radiation. According to a feature essential to the invention,between the catalyst shell and the water-cooled housing is an air gap.Secondary air is drawn from the environment on the downstream end of thecatalyst, guided through the said air gap into an intermediate chamberbetween the reductive and the oxidative catalyst parts and thereexpelled with the exhaust gases. The secondary air introduced via aspecial pump serves, in addition to secondary combustion of the richinjected fuel mixture, also to insulate the very hot catalyst from thecold water-cooled housing parts. The risk of fire on any leakage ofexhaust gas into the boat in the event of a defect in the secondary airfan or secondary air line is eliminated by non-return valves.

The inventor has faced the task of creating a water-cooled catalystsystem of the type described initially which can be used universally forall engine and catalyst types and which requires no additional pipelineswith non-return valves.

SUMMARY OF THE INVENTION

The task is solved according to the invention in that the catalysthousing is surrounded by a gas insulation cover open upstream for theexhaust gas to be detoxified and closed downstream, which has on itsoutside a water cooler lying at least partially thereon. Special andfurther design forms of the invention are the subject of dependentclaims.

The gas insulation cover ending blind in the flow direction of theexhaust gas is of essential significance to the invention. Thissurrounds the catalyst completely with the exception of the outletopening for the detoxified exhaust gases. The inner wall of the gasinsulation cover can be formed by the catalyst housing when sealedaccordingly.

The gas insulation cover, referred to for the sake of simplicity as agas shell, is designed such that the exhaust gases have sufficientclearance upstream to flow unhindered into the catalyst. The gas shellthus extends not only over the peripheral area but also over the area ofthe inlet openings for the catalyst. The gas insulation cover isessentially cup-shaped according to a preferred design variant.

If the gas insulation cover is designed as a double shell in theperipheral area, in the area of the base of the cup the inner wall isomitted or perforated such that the exhaust gas to be cleaned can emergeand flow unhindered into the catalyst.

The inlet and outlet openings of the catalyst may be opposite each otherin the area of the longitudinal axis. If space is limited, for examplein a boat engine, the exhaust gas to be cleaned can be guided into theperipheral shell of the gas insulation cover via an essentiallytangential pipe inlet connector.

The gas insulation cover is suitably designed in the known manner as areflection sound damper of the known type. The outer wall of the gasinsulation cover corresponds to the outer shell pipe of a reflectionsound damper, and the inner wall or catalyst housing corresponds to agas guide pipe in an exhaust system. DE, C1 3810755 describes forexample a reflection sound damper which in principle can also be usedfor a gas insulation cover according to the invention. The arrangementof the gas guide pipes and the intermediate bases is revised accordingto the case.

In contrast to EP, A1 0314129, no secondary air is ever passed to thegas insulation cover. The undetoxified exhaust gases which are guidedinto the gas insulation cover according to the invention are held thereand serve as insulation without an inherent cooling effect. Theaccumulated exhaust gases separate the catalyst housing and the watercooler and the shock effect is damped. The expert has a wide range ofvariants available for the design of the gas insulation cover and watercooler which are defined as a function of the parameters.

The gas insulation cover and the water cooler are suitably made of acorrosion- resistant material easy to machine or mould which has a highheat conductivity at least for the water cooler. In the first placemetals are suitable, in particular copper materials, which are availablein many qualities.

To cool the gas insulation cover on all sides and thus, through theinsulation layer, the catalyst, a water cooler suitably runs all roundbut in certain applications only a specific part need be cooled. Forflat catalysts, for example, the outside in relation to the vehicle canbe cooled whereas the part of the catalyst housing facing the engine hasno cooling water.

In a first variant, the water cooler is designed as a water shell whichlies on the gas insulation cover over its entire surface and isconnected to this, e.g. directly welded, soldered, screwed, riveted,clamped or glued, where in the latter case the layer of adhesive canassume the function of the heat insulating layer.

In a second variant, the water cooler is designed in the form of waterpipes which are connected in principle to the gas insulation cover likea water shell. The pipes can be designed in all conventional shapes ofthe quality concerned, for example round, elliptical, square orrectangular in cross section.

For better heat transmission from the coolant to the water cooler, thismay have longitudinal fins which project into the flow channel but whichoffer the smallest possible resistance to the medium. The fins aresuitably made of the same material as the wall of the water cooler andare welded or soldered to this or co-extruded with this.

The catalyst housing in the gas insulation cover and the external watercooler, which can preferably be drained by activation of a magneticvalve, can easily be mounted in the normal manner for the expert, forexample by screwing, welding, riveting etc.

The catalyst system according to the invention can be operatedparticularly advantageously if a fuelled combustion engine whichgenerates the gas to be cleaned is started with the water coolerdrained, the exhaust gas temperature is measured continuously, and thecooling water is added when a first prespecifiable exhaust gastemperature is reached, a second prespecifiable exhaust gas temperatureis maintained, and after stopping the engine the cooling water isdrained from the catalyst system, where the exhaust gas temperatures aremeasured at the catalyst outlet.

The water-cooled catalyst system is controlled at least partly by ameasuring sensor which projects into the exhaust gas flow on thecatalyst outlet and is connected to a microprocessor. The microprocessorswitches the metering of the coolant water flow fully automatically inthe known manner via actuator elements such as magnetic valves.

The water cooler which is empty when the engine starts allows thecatalyst to have reached an internal temperature of at least 280° C.,corresponding approximately to the first exhaust gas temperature T₁, andthus be ready for operation after 30 to 60 seconds. The coolant watersupply is turned on at the latest when 400° C. is achieved, preferablyin the range from 300° to 350° C. If the exhaust gas temperaturecontinues to rise, cooling water is added in a program-controlled mannersuch that the exhaust gas temperature T₂ fluctuates about a secondprespecifiable value in the range from 450° to 750° C., preferably from480° to 700° C.

The first specifiable exhaust gas temperature T₁ is primarilyengine-dependent, the second specifiable exhaust gas temperature T₂ isengine- and performance-dependent.

It is determined that at full load on a two-stroke boat engine, forexample, an optimum second exhaust gas temperature T₂ is approximately720° C.; at normal load the temperature is from 490° to 520° C. Thecontrol processes are optimised and recorded to be type-specific.

Using this invention, environmentally harmful areas of application forcatalysts which were previously scarcely accessible for economic use canbe accessed in a technically improved way provided that sufficientquantities of the cooling medium water are available. This applies tonew installations and to modifications.

Water-cooled catalysts can be used in connection with two or four-strokepetrol engines and diesel engines; in stationary and mobile variants forships, agricultural and industrial purposes. In boat engines which areof particular interest, the catalyst no longer constitutes a source ofdanger as the surfaces have a temperature in the range from 30° to 50°C. This eliminates not only the risk of fire but also the risk of burnsfrom accidental contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in more detail using the design examplesshown in the drawing which are the subject of dependent claims. Here:

FIG. 1 shows a fuelled combustion engine with a catalyst system,

FIG. 2 shows an outline of a catalyst system,

FIG. 3 shows a side view of a catalyst system according to FIG. 2,

FIG. 4 shows a catalyst with a gas insulation cover and a water cooler,

FIG. 5 shows a catalyst with a serpentine cooling pipe,

FIG. 6 shows a variant similar to FIG. 5,

FIG. 7 shows a catalyst with longitudinal cooling pipes,

FIG. 8 shows a catalyst with annular cooling pipes, and

FIG. 9 shows a cross section through a cooling pipe with fins.

DETAILED DESCRIPTION

In FIG. 1, 10 indicates a fuelled combustion engine fitted with acatalyst 12. The engine has in the conventional manner an exhaust pipewith an exhaust manifold 14 to which is flanged the catalyst 12 by meansof a collar 16. The exhaust gas 18 indicated by an arrow leaves thecatalyst 12 cleaned, with a low residual content of toxic gases. In aboat engine, for example, the engine 10 and catalyst 12 are howeverarranged immediately next to each other and not in successionlongitudinally as shown in principle in FIG. 1. As a catalyst 12, anyconventional catalyst with a steel shell or a catalyst specially adaptedto implement the present invention can be used, the targetedwater-cooled catalyst system being achieved in any case together withthe gas insulation cover and water cooler according to the invention

FIGS. 2 and 3 show a catalyst system 20 of a fuelled combustion engine10 (FIG. 1). The uncleaned exhaust gas 18 is passed to the catalyst 12via a pipe inlet connector 22 with a flange 23. The undetoxified exhaustgas 18 is first passed in approximately tangential direction into theshell chamber of an essentially cup-shaped gas insulation cover form ingap 24 between catalyst housing 40 and the water cooler housing (notnumbered). This gas insulation cover and gap 24 is designed blind in thedirection of the exhaust gas pipe 26 for the cleaned exhaust gas 18'.The uncleaned exhaust gas 18 is passed through the catalyst 12 into theexhaust gas pipe 26. The undetoxified exhaust gas 18 is held in the gasinsulation cover 24 or its shell, and forms, for the surrounding watercooler 28, an insulation layer communicating with the undetoxifiedexhaust gas 18 passed to the catalyst 12.

The cooling water 30 is passed over the cooling shell 32 into the watercooler 28 of the catalyst 12 and from there expelled via the coolingshell 34 of the exhaust gas pipe. The cooling water 30 can also beguided in the reverse direction against the flow.

For exhaust gas extraction before the catalyst, a sealing tap 36 isarranged in flange 23. For exhaust gas extraction after the catalyst, afurther sealing tap 38 is provided in the exhaust gas pipe 26.

FIG. 4 shows a catalyst 12 with a catalyst housing 40 of steel and inseta monolith 42, the active part of the catalyst 12. This monolith 42,also referred to as the carrier body, usually consists of ahoneycomb-like basic body of ceramic or metal of different crosssectional forms. The ceramic material is resistant to high temperatureand in the present case comprises 90% cordierite. This cell carrierrepresents an optimum compromise with regard to:

thermal shock resistance

heat expansion

mechanical strength

large clear cross sectional area and

large geometric surface.

In the catalyst housing 40, consisting of two half shells, transverseribs are formed normally running perpendicular to the longitudinal axisL of the catalyst 12, which ribs are not shown in the present andfollowing figures.

The catalyst housing 40 is surrounded by a gas insulation cover 24formed as a double shell which lies directly on the catalyst housing 40.The cooling water 30 flows under programmed control through a coolingpipe 44 which surrounds the gas insulation cover 24 as a helix. Thegeneral flow direction of the coolant water is here opposite that of theexhaust gas 18.

An inlet connector 50 connected to the inlet hopper 46 of the catalyst12 can, like the outlet connector 52 connected to the outlet hopper 48,be designed in a curved shape which allows for the cramped conditionsfor example of a boat engine.

The inlet connector 50 and the outlet connector 52 are usually connecteddetachably or non-detachably to the corresponding parts of the exhaustsystem.

FIGS. 5 and 6 each show a flat bed, bottle-like catalyst 12. On thefront of both catalysts is a water-filled cooling pipe 44 arranged as aserpentine on the gas insulation cover 24. On the similarly flat back, acooling pipe 44 can also be arranged as a serpentine. In FIG. 6, thestraight pipe sections lie closer together than in FIG. 5 so the coolingeffect is greater while the other parameters remain the same.

In the design form in FIG. 7, the catalyst 12 is cooled by cooling pipes44 lying directly on the gas insulation cover 24 of the catalyst housing40 and running in the axial direction L. These are fed from a lower orupper ring channel 56, 58 where the other ring channel serves as anoutlet.

The catalyst 12, or more precisely its gas insulation cover 24, iscooled according to FIG. 8 by the annular cooling pipes 44 which aresupplied with cooling water through two diagonally opposed verticalconnecting channels 60, where one connecting channel 60 serves as asupply and the other as an outlet.

FIG. 9 shows in cross section a water-filled cooling pipe 44 which hassix fins 54 projecting radially inwards and running axiallylongitudinally. These fins 54, like the cooling pipe 44, are made ofcopper and are co-extruded or welded on. Evidently the fins 54 can alsohave a more complicated geometric shape.

I claim:
 1. A water-cooled catalyst system for reducing emission ofpollutants from exhaust gases from a fueled combustion enginecomprising:a water cooler having a housing defining an internal spaceand having a tangential longitudinal inlet opening for feeding exhaustgases to said internal space and an outlet opening for removing saidexhaust gases from said internal space; a catalyst housing containing acatalyst, said catalyst having an inlet upstream of said catalyst forreceiving said exhaust gases and an outlet downstream of said catalystfor passing said exhaust gases to said outlet opening of said watercooler housing, said catalyst housing being located in said internalspace so as to define with said water cooler housing a cup-shaped gaptherebetween for receiving said exhaust gases so as to surround saidcatalyst housing in an exhaust gas insulation cover prior to passingsaid exhaust gases through said catalyst.
 2. A catalyst system accordingto claim 1 wherein said water cooler housing is flanged to saidcombustion engine.
 3. A catalyst system according to claim 1 whereinsaid water cooler housing defines an internal cooling shell forreceiving a cooling medium for cooling said exhaust gas insulationcover.
 4. A catalyst system according to claim 3 wherein an exhaust gaspipe communicates which said outlet opening and includes an internalcooling passage for receiving said cooling medium from said internalcooling shell.
 5. A catalyst system according to claim 1 wherein saidgas insulation cover acts as a reflection sound damper.